To investigate the possibility of utilizing cancer-testi (CT) antigens as targets for immunotherapy of non-small cell lung cancer (NSCLC) with vaccines.Tissues from 51 NSCLC patients who had chemotherapy prior surgery were assayed for the expression of 11 different CT antigens by RT-PCR.Of the 11 CT antigens analyzed, MAGE-3 was found to be expressed most frequently in NSCLC tissues and CT7 the least frequently. The frequencies of CT antigen expression was: MAGE-3 (38%), NY-ESO-1 (21%), CT10 (17%), LAGE-1 (15%), MAGE-4 (13%), SCP-1, SSX1 and SSX4 (12%), MAGE-1 (10%), SSX2 (6%), and CT7 (2%). Among these cases, 34 (67%) expressed at least one CT antigen gene. 13 of the 17 cases in which no CT antigen expression was found in the tumor tissue, the tumors were classified as at the stage I. MAGE-3 and CT10 were found to be expressed more frequently in tissues from patients with late stage diseases while SCP-1 was found more frequently in earlier stages of NSCLC. CT expression was more frequently found in squamous cell carcinoma than in adenocarcinoma.(1) Cancer vaccines with CT antigens including MAGE-3, NY-ESO-1, LAGE-1, etc, are suitable for immunotherapy of NSCLC after chemotherapy and surgery. (2) NSCLC patients at different stages of disease may be treated with vaccines of different CT antigen composition. (3) CT antigen vaccines are most attractive for patients with late stage NSCLC and/or squamous cell carcinoma of NSCLC.